1. Field of the Invention
The present invention relates to a composite magnetic material capable of being used in a stacked composite device, an inductor or the like for constituting various types of electronic circuits provided in an electronics device such as a cellular phone, and to a method for producing the same.
2. Related Art
In recent years, a demand for downsizing has been increasingly built up in a small-sized electronic device such as a cellular phone. In such a situation, plural electronic circuits constituting an electronic device have been integrated into a stacked composite device on a single chip for mounting on a main substrate.
FIG. 7 is a perspective view showing an example of stacked composite device and FIG. 8 is an exploded perspective view thereof. A stacked composite device, as shown in FIGS. 7 and 8, is constructed by stacking plural ceramic layers 3 and 4. Plural circuit element patterns 11 each including an inductor or a capacitor are formed on surfaces of the ceramic layers 3 and 4. The circuit element patterns 11 are connected to each other by via holes 12 passing through the ceramic layers 3 and 4 or by conductor patterns formed on the ceramic layers 3 and 4, thereby to construct an electronic circuit such as a filter.
It is proposed that in a case where the ceramic layers 3 are magnetic ceramic layers and the ceramic layers 4 are dielectric ceramic layers, a pattern (L pattern) constituting an inductor is formed on each of the magnetic ceramic layers 3 and a pattern (C pattern) constituting a capacitor is formed on each of the dielectric ceramic layers 4 (Japanese Patent Laid Open No. S60-106114, Japanese Patent Laid Open No. H6-333743 and others).
As magnetic materials used in such a stacked composite device and an inductor, there has been generally heretofore used: a NiCuZn-based spinel type ferrite. FIG. 9 is a graph showing frequency characteristics of magnetic permeability of a NiCuZn-based spinel type ferrite. In FIG. 9, there are shown normalized values of a real part μ′ and an imaginary part μ″ of a complex magnetic permeability with the μ′ at 10 MHz as 1. As shown in FIG. 9, the real part μ′ of a complex magnetic permeability takes a comparatively high value in a region up to as high as a value in the vicinity of 100 MHz.
As magnetic materials capable of adapting to higher frequencies, there can be named a hexagonal ferrite. The hexagonal ferrite includes crystal structures of phases which are analogous to each other, such as a Z type, a Y type, a W type and an M type. The phase of the Z type, among them, shows a comparatively high magnetic permeability and reduction in magnetic permeability is minimized in a region up to as high as the GHz band.
FIG. 10 is a view showing a frequency characteristic of magnetic permeability of Z type hexagonal ferrite. In FIG. 10, the real part μ′ and the imaginary part μ″ of complex magnetic permeability are represented by normalized values regarding initial magnetic permeability of NiCuZn-based ferrite (real part μ′ of complex magnetic permeability at 10 MHz) as 1. Also the same applies to the drawings showing frequency characteristics of magnetic permeability explained later.
As shown in FIG. 10, the Z type hexagonal ferrite is superior at high frequency characteristic since the decrease in magnetic permeability is relatively small up to the GHz band. However, the magnetic permeability is lower than that of NiCuZn-based ferrite.
A conventional spinel ferrite such as that of NiCuZn base, as shown in FIG. 9, can be used in a region up to as high as 100 MHz, whereas a natural resonance occurs in a region of higher frequencies to decrease a real part μ′ of magnetic permeability but to contrary to this, increase an imaginary part μ″ thereof (which is a Snoek limit). In addition, in the Z type hexagonal ferrite, there is a problem that the value of magnetic permeability is lower than that of the NiCuZn-based ferrite, while decrease in magnetic permeability is small up to the GHz band and hence it is superior at high frequency characteristic as described above.
Accordingly, in the conventional magnetic materials, it was difficult to achieve both of high magnetic permeability and excellent high frequency characteristic. Also, it was difficult to design the value and the frequency characteristic of magnetic permeability of the magnetic material at will.